Pre-emptive air dryer control in a compressed air system

ABSTRACT

A fluid compression system includes a compressor operable to produce a first flow of compressed fluid and a refrigerated dryer coupled to the compressor and operable to separate the first flow of compressed fluid into a second flow of compressed fluid and a flow of liquid. A first sensor is positioned to measure a property of the second flow of compressed fluid, and a controller is operable to initiate operation of the refrigerated dryer at a first time and at least partially in response to the measured property, and to initiate operation of the compressor at a second time. The first time is before the second time.

CROSS-REFERENCE TO RELATED APPLICATION

The present application claims the benefit of U.S. Provisional Application No. 60/881,307 filed Jan. 19, 2007. The prior application listed in this paragraph is hereby incorporated by reference in its entirety.

BACKGROUND

The present invention relates to a compressor system, including an air dryer, and more particularly to a compressor system including an air dryer having a pre-emptive air dryer control.

Air dryers are typically used in compressed air systems to remove water, lubricant, water and lubricant vapors and other contaminants from the air after the air is compressed and discharged from the air compressor. There are a variety of air dryers available to accomplish this function.

One type of air dryer is a cycling refrigerated dryer which cycles on and off to maintain its refrigerant at a specified temperature for cooling the compressed air. These air dryers are typically turned on and off with the air compressor such that the air dryer is started and stopped by the air compressor controls. In this manner, the air dryer remains off as long as the air compressor drive (e.g., motor, engine, etc.) is not running. Likewise, the air dryer is started when the air compressor is started.

SUMMARY

Some air compressor systems supply air to a process intermittently and as such, the air compressor and dryer may be turned off for long periods of time. When the air compressor and dryer have been turned off for a long period of time, the dryer's refrigerant temperature can rise significantly above its optimum operating value. When compressed air is needed, the air compressor and the air dryer are restarted. However, after being turned off for a long period, it takes the air dryer a certain amount of time to cool its refrigerant back to its optimum operating temperature and to effectively remove moisture and contaminants from the compressed air. During the time period the air dryer refrigerant is being cooled, some amount of air supplied to the air system may not be dried to a desired level.

One construction of the invention provides a fluid compression system that includes a compressor, a refrigerated dryer, a sensor, and a controller. The compressor produces a flow of compressed fluid, which in the preferred construction is air which may contain water vapor or other fluid (e.g. lubricant). After the compressed air leaves the compressor it is considered wet air due to the presence of water vapor. The wet air is then cooled by the refrigerated dryer and the wet air is split into a second flow of compressed fluid (dry air) and a flow of fluid (water). The water is expelled from the system and the dry air passed to a point of use, which may be a storage tank, air hammer, etc. The sensor is positioned such that it measures a property of the system and the controller initiates and stops the compressor and the refrigerated dryer at least partially in response to the property measured by the sensor. In the preferred construction, the refrigerated dryer starts prior to the compressor such that no wet air is directed to the point of use.

In another construction the invention provides a fluid compression system that includes a compressor operable to produce a first flow of compressed fluid and a refrigerated dryer coupled to the compressor and operable to separate the first flow of compressed fluid into a second flow of compressed fluid and a flow of liquid. A first sensor is positioned to measure a property of the second flow of compressed fluid, and a controller is operable to initiate operation of the refrigerated dryer at a first time and at least partially in response to the measured property, and to initiate operation of the compressor at a second time. The first time is before the second time.

In another construction, the invention provides a method of operating a fluid compression system. The method includes measuring a first parameter of a compressed fluid, starting a refrigerated dryer system at least partially in response to the first measured parameter, and measuring a second parameter after starting the refrigerated dryer system. The method also includes starting a compressor at least partially in response to the second parameter.

In yet another construction, the invention provides a method of operating a fluid compression system that delivers compressed fluid to a point of use. The method includes measuring a property of the compressed fluid at the point of use with a first sensor, initiating operation of a refrigerated dryer at least partially in response to the measured property, and initiating operation of a compressor after initiating operation of the refrigerated dryer. The compressor is operable to produce a first flow of compressed fluid. The method also includes directing the flow of compressed fluid to the refrigerated dryer, separating the first flow of compressed fluid into a second flow of compressed fluid and a flow of liquid using the refrigerated dryer, and stopping operation of the compressor and the refrigerated dryer at least partially in response to the measured property.

Other aspects of the invention will become apparent by consideration of the detailed description and accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic representation of a fluid compression system according to the invention;

FIG. 2 is a graph of pressure versus time during operation of the fluid compression system according to one construction of the invention;

FIG. 3 is a flow chart illustrating a portion of a first control scheme;

FIG. 4 is a flow chart illustrating a portion of a second control scheme;

FIG. 5 is a flow chart illustrating a portion of a control scheme that follows either the first control scheme or the second control scheme;

FIG. 6 is a flow chart illustrating a portion of an alternative control scheme that follows either the first control scheme or the second control scheme.

Before any constructions of the invention are explained in detail, it is to be understood that the invention is not limited in its application to the details of construction and the arrangement of components set forth in the following description or illustrated in the following drawings. The invention is capable of other constructions and of being practiced or of being carried out in various ways. Also, it is to be understood that the phraseology and terminology used herein is for the purpose of description and should not be regarded as limiting.

DETAILED DESCRIPTION

FIG. 1 illustrates one possible arrangement of a fluid compression system 10 that includes a compressor 14 and a refrigerated dryer 18 that cooperate to provide dry compressed fluid or gas to a system or point of use 22. In a preferred construction, the point of use 22 includes a tank, a reservoir, and the like. However, in alternate constructions, the point of use 22 may include one or more injection molding machines, pneumatic equipment, pneumatic tools, pneumatic actuators, pneumatic controls, and the like. In addition, the fluid or gas is preferably air although other fluids or gases have been considered.

The compressor 14 may include a single compressor or a plurality of compressors arranged in parallel and/or series to output a flow of compressed air at a desired flow rate and pressure. In addition, the compressor 14 may include a rotary compressor such as a rotary screw compressor, a centrifugal compressor, a reciprocating compressor, or another compressor design or combinations thereof. Thus, the invention should not be limited by the type, quantity, or arrangement of the compressor 14 or compressors.

The refrigerated dryer 18 of FIG. 1 includes a refrigerant compressor 26, an evaporator 30, an expansion device 34, and a condenser 38 arranged in a manner similar to a standard refrigeration cycle. The refrigerant compressor 26 may include one or more compression devices that are suited to compressing a refrigerant to produce a flow of refrigerant. For example, one or more rotary screw compressors and/or one or more scroll compressors could be employed as the refrigerant compressor 26. Of course, other types of compressors or combinations of compressors not described herein could be employed as refrigerant compressors 26 if desired.

The condenser 38 cools the refrigerant to remove a portion of the heat of compression. In the illustrated arrangement, a fan 42 is employed to cool the refrigerant. The fan 42 may be operated continuously, intermittently, or at variable speeds to achieve the desired level of cooling of the refrigerant. In preferred constructions, at least a portion of the refrigerant condenses within the condenser 38 such that a flow of liquid refrigerant exits the condenser 38. As one of ordinary skill in the art will realize, many heat exchanger designs could be employed in the condenser 38. For example, finned-tube heat exchangers, shell and tube heat exchangers, plate-fin heat exchangers, micro-channel heat exchangers, and the like could be employed within the condenser 38. Thus, the invention should not be limited by the type of heat exchanger employed.

The expansion device 34 is positioned downstream of the condenser 38 such that it receives a flow of high-pressure liquid refrigerant that has passed through the condenser 38. The expansion device 34 causes a rapid expansion of the refrigerant which produces a corresponding drop in the temperature of the refrigerant after it exits the expansion device 34.

Operating as a standard refrigeration cycle, the system 18 produces a flow of cool refrigerant through the evaporator 30. Compressed air supplied by the air compressor 26 flows through the evaporator 30 and is cooled by the refrigerant. The water vapor in the compressed air condenses in the air stream and is separated and removed from the compressed air using a liquid-gas separation device 46. This process produces a flow of dry compressed air and a flow of liquid. While many liquid-gas separation systems are possible, mechanical separation that relies on variations in the mass and inertia of the liquid and gas such as cyclone-type separators are preferred. Of course, other separators such as coalescing filters can be used in conjunction with or in place of the mechanical separation device. As such, the invention should not be limited to one type of separation system.

The air then passes through a recuperator 50 where it is heated slightly such that the exiting air stream at an air outlet 54 is at a temperature above its dew point. The recuperator 50 includes a heat exchanger that receives the hot flow of compressed air from the compressor 14 and discharges a pre-cooled flow of compressed air. The heat exchanger also receives the flow of cool dry compressed air and heats it such that the discharged dry air is at a temperature well above its dew point temperature, thereby reducing the likelihood of additional condensation during use. Thus, the recuperator 50 reduces the load on the evaporator 30 by pre-cooling the incoming air, thereby allowing for a smaller evaporator 30 and/or refrigerated dryer 18. As one of ordinary skill in the art will realize, many different heat exchanger arrangements, including finned-tube heat exchangers, shell and tube heat exchangers, plate-fin heat exchangers, micro-channel heat exchangers, and the like may be employed in the recuperator 50.

As one of ordinary skill in the art will realize, other components or systems that are commonly employed in refrigeration systems could also be employed in the present arrangement. For example, a vessel could be positioned in the cycle to collect excess refrigerant and serve as a reservoir. Additionally, check valves, sensors, and controls could be positioned at various points along the refrigerated dryer 18 if desired.

FIG. 2 graphically illustrates the operation of one construction of the system of FIG. 1. A controller 60 monitors the fluid compression system 10 to determine when to start or stop the compressor 14. The controller 60 also controls operation of the refrigerated dryer 18. In preferred constructions, the controller 60 employs a base control scheme that allows for starting the refrigerated dryer 18 before starting the compressor 14. Each of the base control schemes includes several variations that can be employed in any of the base control schemes as may be required by the particular application.

One base control scheme (partially illustrated in FIG. 3) employs the controller 60 to monitor the fluid compression system 10 with a sensor 58 to determine when to initiate operation of the compressor 14. The sensor 58 can be a sensor adapted to measure pressure, rate of change of pressure, temperature, time, or other properties and can be positioned upstream or near the point of use 22, such as within the reservoir or tank. In the preferred construction, sensor 58 is a pressure sensor. When the sensor 58 detects that the pressure within the fluid compression system 10 has fallen below a pre-determined threshold level, the refrigerated dryer 18 is started. For example, in one system it is desirable to supply compressed air between 100 pounds per square inch (psi) (0.69 MPa) and 120 psi (0.83 MPa). In this system, the operation of the refrigerated dryer 18 could be started when the measured pressure falls below 105 psi (0.72 MPa). The refrigerated dryer 18 would then operate until the compressor 14 started operation and would continue to operate throughout the operating period of the compressor 14. The pressure at which the refrigerated dryer 18 starts can be adjusted based on the particular system to assure that the refrigerant reaches the desired temperature just as the compressor 14 starts operation. The sensor 58 generally measures the air pressure at the point of use 22. However, the air pressure may be measured at one or more locations within the system by use of one or more sensors 58. In addition, the one or more sensors 58 may measure any number of properties and combinations of properties, such as time and rate of change of pressure.

Operation of the refrigerated dryer 18 may be initiated at a pressure that allows for a specified amount of time for the refrigerant to cool before the compressor 14 is operated. In an alternative arrangement, the refrigerated dryer 18 is operated for a specified amount of time to allow the refrigerant to reach a specific temperature before operation of the compressor 14 is started. Thus, a timer 62 is employed to start the compressor 14 after the passage of a predetermined period of time following the start of the dryer 18. This arrangement assures that the refrigerant reaches the desired temperature and reduces the amount of time the refrigerated dryer 18 operates without operation of the compressor 14. In other constructions, a second measured pressure is employed to start the compressor 14. In these constructions, the timer 62 can be used to shutdown the dryer 18 if the compressor 14 does not start in a predetermined time period. Thus, the dryer 18 will operate until the pressure falls below a second predetermined pressure at which point the compressor 14 starts. In still other constructions, a temperature sensor measures a temperature within the dryer 18 and starts the compressor 14 when the measured temperature reaches a desired temperature.

The first control scheme can be used with one compressor 14 or a plurality of compressors. The controller 60 can monitor the fluid pressure within the compression system 10 via sensors 58 and operate the refrigerated dryer 18 and the compressor 14 as necessary. In another alternative arrangement, the refrigerated dryer 18 operates for a specific amount of time such that the refrigerated dryer 18 will stop after a pre-determined amount of time if the compressor 14 does not start. This arrangement assures that the refrigerated dryer 18 will not operate longer than the necessary demands of the compressor 14 would dictate.

Another base control scheme (partially illustrated in FIG. 4) employs the controller 60 to monitor the rate-of-change of the air pressure at one or more measuring points in the fluid compression system 10. The air pressure can be measured by the sensor 58 located virtually anywhere within the fluid compression system 10 with a measurement at the point of use 22 being preferred. The controller 60 uses the measured air pressure and the rate-of-change of the air pressure to predict when the compressor 14 will need to be operated for additional compressed air. Using the above-described example, if the refrigerated dryer 18 requires five minutes to cool the refrigerant to the desired level and the measured rate of change of the pressure in the fluid compression system 10 is 1 psi (0.007 MPa) per minute, the controller 60 will start the refrigerated dryer 18 when the measured pressure is 5 psi (0.034 MPa) above the desired minimum pressure.

As with other control schemes described herein, the refrigerated dryer 18 operates continuously until the pressure reaches the level at which the compressor 14 begins operation. The refrigerated dryer 18 and the compressor 14 then preferably operate until the compressor 14 is stopped. In an alternative construction, the refrigerated dryer 18 may be started as described. However, in addition to starting the refrigerated dryer 18, a timer 62 may initiate to control the start of the compressor 14 such that the compressor 14 begins operating a predetermined time after the start of the refrigerated dryer 18. In still other constructions, a temperature sensor measures a temperature within the dryer 18 and initiates operation of the compressor 14 when the temperature reaches a desired value.

In some constructions, a second sensor monitors a temperature within the refrigerated dryer 18. For example, the second sensor could measure the refrigerant temperature anywhere within the refrigerated dryer 18 such as downstream of the refrigerant compressor 26 or could measure the temperature within the evaporator 30. This second measured property could be used to calculate the amount of time the refrigerated dryer 18 needs to reach the desired operating temperature. This calculated time could be used to vary the pressure at which the refrigerated dryer 18 starts operation. Such a measurement could be employed using any control scheme described herein.

FIGS. 3-6 illustrate portions of some of the control schemes discussed herein. Of course many different variations are possible and may be suitable for use. For example, one alternative incorporates a temperature measurement taken from the refrigerated dryer 18 that is then used in an algorithm to vary the starting pressure of the refrigerated dryer 18. Thus, when the refrigerated dryer 18 is hotter, it will run longer to achieve the desired level of cooling before starting the compressor 14.

The additional amount of time for the refrigerated dryer 18 to operate before the compressor 14 is started allows the evaporator 30 to cool in advance of operation of the compressor 14 such that air is effectively dried beginning at the time the compressor 14 starts. This avoids a spike in dew point of the system air. In each control scheme, the compressor 14 is not delayed in operating, rather the refrigerated dryer 18 is started a pre-determined amount of time before the compressor 14 is needed.

In some constructions, the refrigerated dryer 18 is controlled independent of the compressor 14 such that the refrigerated dryer 18 is operated for a pre-determined amount of time and stops automatically regardless of whether or not the compressor 14 is operated.

In operation, and as illustrated in FIG. 3, one system measures a pressure at block 300. Preferably, the pressure is measured at or near the point of use. The measured pressure is then compared to a first predefined pressure value or a dryer start pressure at block 305. If the pressure is not below the dryer start pressure, the measurement is retaken and the new measured pressure is compared to the first predefined pressure. If the measured pressure falls below the first predefined pressure, the control starts the dryer (block 310) and moves to the steps illustrated in FIG. 5 or FIG. 6.

With reference to FIG. 5, the control starts a timer 62 (block 315) after the start of the dryer and continues to measure the pressure at block 320. The measured pressure is compared to a second predefined value or a compressor start value at block 325. In addition, the timer 62 value is compared to a predefined time limit at block 330. If the timer 62 reaches the predefined time limit before the pressure reaches the second predefined value, the dryer is stopped (block 335). However, if the pressure falls below the second predefined pressure before the timer 62 reaches the predefined time limit, the compressor is started (block 340). The pressure is then measured and compared to a third predefined pressure or compressor stop pressure (blocks 345 and 350). When the pressure reaches the third predefined pressure, the dryer and the compressor are stopped (block 355) and the control returns to the status of FIG. 3.

In some constructions, the timer 62 is used to start the compressor rather than to stop the dryer. In this construction, illustrated in FIG. 6, the timer 62 is monitored (block 330) until it reaches the predetermined time, at which point the compressor is started (block 340). In yet another construction, the timer 62 is eliminated and the pressure is used to start the compressor. In this construction, the pressure is monitored until it reaches the third predetermined pressure, at which point the compressor is started (block 340). In still another construction, a temperature of the dryer is measured rather than the pressure. In this construction, the compressor is started at block 340 when the measured temperature falls below a predetermined temperature. Thus, blocks 315 and 330 of FIG. 6 can be replaced with temperature measurement and comparison blocks or pressure measurement and comparison blocks if desired.

In another construction, the control system monitors the system as illustrated in FIG. 4. In this construction, the control system measures an initial pressure at block 300 and then measures a subsequent pressure some time later (block 360). The two measured pressures are then used to determine a rate of change of pressure as illustrated at block 365. The rate of change and the last measured pressure are then provided to an algorithm that estimates when the compressor and the dryer will need to be started (block 370). If the algorithm determines that the dryer should be started (block 375), the control transitions to the steps illustrated in FIG. 5 or FIG. 6. If the algorithm does not require the start of the dryer, a new pressure is measured and the process continues.

It should be noted that some constructions also monitor a temperature of the dryer to estimate how long it will need to operate to reach a desired operating temperature. In these constructions, the dryer may start earlier or later depending on its temperature. The algorithm of block 370 could account for this input.

It should be noted that the term “dry air” is used herein to describe air that has passed through the refrigerated dryer 18. However, as one of ordinary skill in the art will realize, dry air is not devoid of water or water vapor. Rather, dry air is air that has had a portion of the moisture removed to reduce the likelihood of additional moisture condensing from the compressed air during use.

Thus, the invention provides, among other things, a fluid compression system that delivers compressed dry fluid or gas to a system or point of use. Various features and advantages of the invention are set forth in the following claims. 

1. A fluid compression system comprising: a compressor operable to produce a first flow of compressed fluid; a refrigerated dryer coupled to the compressor and operable to separate the first flow of compressed fluid into a second flow of compressed fluid and a flow of liquid; a first sensor positioned to measure a property of the second flow of compressed fluid; and a controller operable to initiate operation of the refrigerated dryer at a first time and at least partially in response to the measured property, and to initiate operation of the compressor at a second time, wherein the first time is before the second time.
 2. The fluid compression system of claim 1, wherein the sensor includes a pressure sensor and the measured property includes a pressure.
 3. The fluid compression system of claim 1, wherein the first flow of compressed fluid includes a mixture of air and a first amount of water vapor.
 4. The fluid compression system of claim 3, wherein the second flow of compressed fluid includes air and a second amount of water vapor, the second amount of water vapor being less than the first amount of water vapor.
 5. The fluid compression system of claim 4, wherein the flow of liquid includes condensed water vapor removed from the first amount of water vapor.
 6. The fluid compression system of claim 1, wherein the controller is operable to stop the refrigerated dryer and the compressor at least partially in response to the measured property.
 7. The fluid compression system of claim 1, wherein the controller is operable to start the compressor at least partially in response to the passage of a predetermined length of time after the first time.
 8. The fluid compression system of claim 1, wherein the controller is operable to stop the refrigerated dryer and the compressor substantially simultaneously.
 9. The fluid compression system of claim 1, wherein the measured property is a rate of change of pressure.
 10. A method of operating a fluid compression system, the method comprising: measuring a first parameter of a compressed fluid; starting a refrigerated dryer system at least partially in response to the first measured parameter; measuring a second parameter after starting the refrigerated dryer system; and starting a compressor at least partially in response to the second parameter.
 11. The method of claim 10, wherein the first parameter is a pressure.
 12. The method of claim 11, wherein the second parameter is a pressure.
 13. The method of claim 11, wherein the second parameter is a temperature.
 14. The method of claim 10, wherein the first parameter is a rate of change of pressure.
 15. The method of claim 10, wherein the second parameter is a passage of time from the start of the refrigerated dryer system.
 16. The method of claim 10, wherein the second parameter is the same as the first parameter.
 17. A method of operating a fluid compression system that delivers compressed fluid to a point of use, the method comprising: measuring a property of the compressed fluid at the point of use with a first sensor; initiating operation of a refrigerated dryer at least partially in response to the measured property; initiating operation of a compressor after initiating operation of the refrigerated dryer, the compressor operable to produce a first flow of compressed fluid; directing the flow of compressed fluid to the refrigerated dryer; separating the first flow of compressed fluid into a second flow of compressed fluid and a flow of liquid using the refrigerated dryer; and stopping operation of the compressor and the refrigerated dryer at least partially in response to the measured property.
 18. The method of operating the fluid compression system of claim 17, wherein the property is a pressure.
 19. The method of operating the fluid compression system of claim 17, wherein the property is a rate of change of pressure.
 20. The method of operating the fluid compression system of claim 17, further comprising monitoring the passage of time from the initiation of the dryer and initiating operation of the compressor after the passage of a predetermined period of time.
 21. The method of operating the fluid compression system of claim 17, wherein the step of stopping the compressor and the refrigerated dryer includes stopping the compressor and the refrigerated dryer substantially simultaneously.
 22. The method of operating the fluid compression system of claim 17, further comprising measuring a temperature of the refrigerated dryer and starting the compressor at least partially in response to the measured temperature.
 23. The method of operating the fluid compression system of claim 17, further comprising remeasuring the property and starting the compressor at least partially in response to the remeasured property. 